Vibrating, rotating and/or stationary screens are used in the oil sand industry, in particular, in oil sand slurry preparation plants. Oil sand, such as is mined in the Fort McMurray region of Alberta, generally comprises water-wet sand grains held together by a matrix of viscous bitumen. It lends itself to liberation of the sand grains from the bitumen by mixing or slurrying the oil sand in water, allowing the bitumen to move to the aqueous phase.
As-mined or pre-crushed oil sand is generally mixed with warm or hot water to yield an oil sand slurry. The slurry is then conditioned in a hydrotransport pipeline and subsequently introduced into a large, open-topped, conical-bottomed, cylindrical vessel commonly termed a primary separation vessel (PSV) where the more buoyant aerated bitumen rises to the surface and forms a bitumen froth layer.
It may be desirable to remove the larger aggregates present in oil sand slurry prior to pipelining in order to avoid blockage or damage of downstream equipment, e.g., pump component wear. Thus, vibrating, rotating and/or stationary screens may be used at various points during slurry preparation to reject larger lumps of oil sand, rocks and other aggregates, which are large enough to block or damage downstream equipment, prior to pipeline conditioning. Screens may also be used to further screen oil sand tailings slurry prior to treating/disposing same.
However, oil sand slurry is extremely heavy and abrasive due to the large amount of sand, gravel and crushed rock contained therein. Further, in particular with primary vibrating screens, these screens are generally vibrating with an acceleration of approximately 4-5 g, so that all oil sand slurried material passes over and through the screen cloths of the vibrating screen. This results in the rapid spalling and eventual wearing through of the screen cloths of the vibrating screen (“hole-throughs”), which can lead to production interruption and an unplanned maintenance event.
Various types of screen cloths are currently used. Hard-faced screen cloths such as tungsten carbide overlays provide excellent resistance against abrasion wear, but often prematurely fail due to impact and fatigue damage. Elastomer-lined screen cloths exhibit improved wear performance due to their energy-dampening capability through elastic deformation; however, when the impact energy of oversize reject material is beyond the elastic capability of the elastomers, tearing or gouging occurs. Despite the availability of different types of screen cloths, poor wear capability and plugging remain persistent problems in screening.
Thus, it is desirable to have an improved screen cloth that can withstand the abrasiveness of oil sand slurry.